texts: Secular parallax calculation in Binney and Merrifield

texts:
I am now reading Galactic Astronomy (1998) by Binney and Merrifield. In this book at p. 44 there is this formula for calculating proper motion vector:
$$\boldsymbol\mu_i = \frac{(\mathbf u_i \times\hat{\mathbf x}_i)\times\hat{\mathbf x}_i}{x_i},$$
where $\mathbf u_i$ is stellar heliocentric velocity, $x_i$ is stellar distance and $\hat{\mathbf x}_i$ is stellar unit position-vector. When using this formula, I found that the proper motion has direction opposite to the stellar velocity (because of two multiplication with position-vector). Wouldn't it be intuitive that the motion has the same direction as the velocity? Did I miss something?
Also, using this illustration:

component of proper motion vector that is parallel to great circle connecting stellar position-vector $\hat{\mathbf x}_i$ and solar velocity vector $\hat{\mathbf v}_\odot$ could be found by,
$$\mu_{\parallel i} = \frac{\boldsymbol \mu_i \cdot \hat{\mathbf v}_\odot}{\sin{\psi_i}}.$$
I do not see why this is the case. Could someone please give me some hints?


texts: Question regarding the path of sun crossing zenith before the summer solstice

texts:
I stay in Bangalore, India (12.9716° N, 77.5946° E). For my latitude, the Sun crosses zenith (the highest point in the sky) on 24th of April every Summer, which happens to be about 2 months prior to the June solstice (summer solstice to us here in the Northern Hemisphere).

Shouldn't the Sun be reaching its highest point on the longest day, i.e. on June 21st, instead of April 24th?
Doesn't the Sun take the longest arc across the sky on the day it passes through zenith?

For reference, the angle at which the Sun rises/sets in my location is about 13 degrees, which happens to be almost vertical to the horizon.


texts: Hydrogen Line observation - Interference from trees

texts:
I am setting up a 2.4 metre parabola pointing straight up to observe the 21cm hydrogen line at 1420MHz with meridian drift scans.

I'm planning to place the dish on a steel pole embedded in the ground and protruding 2 metres from the ground surface.

There is a tree some metres away that has a few branches well overhead of the antenna.  It's a Eucalyptus tree, so not heavy with green leaves.

Question:  Should I be concerned about interference from a few overhanging branches (say about 15 metres above the dish)?  My understanding is that shorter lines in the cm range should be less affected by interference (e.g weather), but I'm not sure about trees.


texts: Why would the side of the moon that faces earth be as dark as the far side of the moon?

texts: Somebody suggested that the side of the moon that always faces the earth is as dark as the far side of the moon, but is that really the case? Doesn’t earth-shine make the earth-facing side of the moon overall brighter? Or does the absence of a moon atmosphere negate any possible gain from earth-shine?


texts: How long does it take for a galaxy (or other object) to disappear behind the cosmic sight horizon?

texts:
After looking at this question, I am wondering, how long does it take for a galaxy or other space object, to disappear from our view from the Milky Way due to the expansion of the universe? Assume GN-z11 is our target object here, or some other notable distant object.
Edit: As @PM2Ring said in a comment, "No galaxy that is observable today ever disappears (but does become increasingly redshifted." So when does a target galaxy get so redshifted that we cannot see it anymore?


texts: Is mass+energy conserved when a new universe forms inside a black hole?

texts: My understanding is that there are credible theories out there in which the formation of a singularity in a black hole also represents the beginning of a new universe via a big bang. We can't see the new universe because we can't see anything from within a black hole. Further, the apparent size of the black hole to us does not have to equal the size of the new universe from the perspective of someone inside that universe. My question is, is mass+energy conserved? That is, is the total amount of material within the new universe limited to how much stuff has fallen into the black hole, or how much stuff has reached the singularity? If so then it would seem these black hole universes are only a tiny fraction the size of our own universe.


texts: I was wondering what a phone call would be like entering or falling t=into a black hole. Due to the massive density of the black hole and time would feel slower, how would that appear to the person on the other side of the call?


texts: What happens with the black hole's mass when a black hole disappears?

texts: If a black hole isn't "fed" by attracted matter, it disappears someday. But how is that even possible? What happens with the mass at its singularity? It can't just disappear or am I wrong with something? Where does the mass disappear to and how is it possible?


texts:
Given that some exoplanets, particular "Hot Jupiters", orbit very closely to their parent star, how hot can these planets become?

What is the hottest exoplanet discovered so far?


texts: How can we be certain that Ryugu is a remnant of the material that did not form planets?

texts:
As mentioned here, that Ryugu is a part of the Solar System material that did not get swept into forming a planet.

But how can we be sure that it was not created later for example by an asteroid striking Mars or some other planet? Why do we think its "primordial"?


texts: Amateur radioastronomy: dish suggestions

texts:
What kind of amateur radioastronomy can any interested citized do with:

a) A 2 m dish antenna.
b) A 2,5 m antenna.
c) A 3 m antenna.
d) A 5 m antenna.
e) A >5 m <10 m antenna (likely I can not afford this or the previous but I just want to know...).

Of course, space is sometimes a logistic issue for big stuff, but I wondered what kind of objects or sources can someone do with suitable instruments and with aid enough if not an expert. Projects and links would be welcome!


texts: What leads to increase in opacity in kappa mechanism?

texts:
I understand that the kappa mechanism (that leads to star variability) causes an increase of opacity with increasing temperature in partial ionization zones.  However, I'm not sure I understand what causes the increasing opacity with temperature.

Until recently, I thought that the increasing opacity was due to increasing Thompson opacity due to the increasing ionization fraction with temperature in partial ionization zones.  However, some things I read suggested that that was not the cause.  So I wanted to ask, what is the cause of increasing opacity with temperature in partial ionization zones?


texts: Can the expansion of spacetime be directly measured with laser interferometry (like GW can)

texts: LIGO has a mind boggling sensitivity. What would it take to directly measure the expansion of spacetime, along the laser beam? I suppose it could be done at interplanetary scale.


texts: Open access table of visible stars with magnitude, coordinates, and possibly color?

texts:
I'm looking for a link to a table of visible stars that is open and available to everyone. It should have magnitude, RA, dec, and possibly some indication of color. This will be used to produce somewhat realistic night skies as a backdrop for showing the motion of the planets in the sky.

I'm not so interested in names, constellations, etc. These are of course useful to know and possibly to plot, but what I'm primarily after is the information necessary to illustrate star position, brightness, and some color information.

edit: to reiterate, "...table of visible stars that is open and available to eveyone." I'm assuming that in 2016 the visible stars are not behind a paywall, am I wrong? Approx RA, dec, mag - are these available for open access and usage?


texts: How deep in Mars would a person not need insulation and pressure?

texts: How deep in Mars' surface would one have to go to both not need a pressurized suit and be warm enough to just wear clothes? in other words is there a dept Goldilocks where you would only need an oxygen supply?


texts: What is meant by Electronic Beam Steering and how is it achieved?

texts: I recently came across an article about the Murchison Wide Field Array which said directivity is achieved by Electronic Beam Steering and not by Mechanical methods. It would be helpful if someone can tell me: how do they achieve it?


texts: Assuming no light pollution, was "2C. 1406" ever visible to the naked eye?

texts:
Joseph Needham, in his Science and Civilisation in China Vol. III, claimed that there was an ancient record of a nova about three thousand years ago. As a result of private correspondences with a "Dr A. Beer" (maybe Arthur Beer?), Needham stated in his book that

  This supernova position ["position" being "next to Antares"] agrees closely with the radio-star 2C. 1406.

Assuming that "2C. 1406" refers to an item in the Second Cambridge Catalogue of Radio Sources, the data given for this item (original document here) is

Acknowledging that the Second Catalogue has various problems, my questions are:

Is "2C. 1406" (still) considered to be "IC 4606" (which, I suppose, refers to this nebula from the SIMBAD Astronomical Database)?
If so, was "IC 4606" ever visible to the human eye?
If not, what do the coordinates given for "2C. 1406" currently refer to (if anything), and was this ever visible to the naked eye? Or is this not really a radio source, but an error that was fixed by later Catalogues?

Note, the interpretation of the supposed nova record is extremely controversial, so I wouldn't be surprised if the text didn't refer to any kind of astronomical observation at all.


texts: Why can't we point the centre of the universe from inflation graph we see?

texts:
This question is not about whether it makes sense to have a centre of the universe or not instead, it's about the inflation graph we used to see while describing the Big Bang. From the inflation graph (drawn above), it's clear that the universe is supposed to have a centre at somewhere around "The yellow point". Still why do we say that the universe has no centre or universe has it's centre at each point of it.
What's the problem with the figure or my understanding?


texts: strange moonset around 10 pm (3.2 2014, NZ) - explanation?

texts:
during a visit to New Zealand we observed (on 3.2 2014) a strange moonset in Te Anau.

Around 10 pm, shortly after sunset, the moon appeared, but then quickly began to go down, and about 1 hour or less it "touched" the mountains on horizon and shortly after it completely disappeared and then we did not see it anymore.

I did not bring a camera or camcorder, so I only have this bad photo from a mobile phone:

The whole process was pretty fast, so I only have one picture. I've never seen anything like it - usually (in Europe) the moon comes out after sunset rather than going down :-)

There was also one guy living there more than 10 years, but he was apparently surprised too.

Can anybody explain this? Is it something normal in this location?

thanks


texts: Are the sub-spectral types (1,...9) based on temperature or spectral lines?

texts: The spectral type of stars has an OBAFGKM class, along with a number, from 0 to 9. According to Wikipedia, (sample shown below), the lower the number, the hotter and more massive the star, but absorption lines are not included. Then looking at the second image, we can see that different spectral types have different absorption lines. So I am wondering, are the sub-spectral types (numbers) based off of temperature and/or mass or absorption/spectral lines?


texts:
After origin of Earth ( 4.54 billion years ago ) to today; what are the changes  through-which the sun undergone with time? , ( if seen from Earth. )

I'm doing some palaeobiology-landscape rendering; so I'm thinking if I want to add the sun in such pictures; should I draw it just like present day? Or the look/ appearance (colour, size, flames, position, halo etc) varied in observable amount through the geologic time-scale(precambrian-cambrian-ordovician-silurian-devonian-carboniferous-permian-triassic-jurassic-cretaceous-palaeogene-neogene etc). (the timescale terms provided just to hint the answerer the level of details may NOT to go )

Update: Here I attach a  small version of geologic time table to indicate time ranges.

from here .

To see the entire chart; see international commission of stratigraphy charts


texts: Can white dwarfs have accretion discs too?

texts: Neutron stars and black holes can have discs of accreted matter for they have an extremely high gravitational pull. While white dwarfs don't have such high gravity theirs is of course also extremely strong. Can an accretion disc form around a white dwarf too?


texts: What are the odds that the Sun hits another star?

texts: The Sun moves around the Milky Way disk in the same direction as most of the other stars in our galaxy (prograde).  But there are a number of older stars in the galactic halo that move in retrograde orbits, and some of them pass between the Sun and the center of the galaxy.  What are the chances that the Sun will collide with another star, say in the next 5 billion years?


texts: Can massive objects pull photons into existence?

texts:
When a photon tries to leave a black hole, it is redshifted until the wave length is infinite and the photon disappears(?).
Could this also happen the other way round, that a (non existent) photon with an infinite wave length is blueshifted into existence by a massive object?
If that's true could this explain the background radiation?
I mean that we see radiation within our galaxy that comes from the outside, but does not really exists outside, because on the outside the wave length of this radiation is infinite.


texts: Why is the asteroid belt shaped like a triangle?

texts:
So, in this question, the user JollyJoker posted this image depicting the orbits of the asteroids in the asteroid field in the comments:

[

In this image, you can see that while the individual asteroids follow elliptical orbits, the asteroid belt as a whole is a giant triangle with the Jovian Trojans at two corners, and a third corner directly opposite Jupiter, and the whole triangle orbits in sync with Jupiter.

Is this image accurate? Is the Asteroid Belt actually a giant triangle, rather than the loose circle it is often depicted as? If so, why is this the case?


texts: Researching mechanics without “fixed stars”

texts:
In the history of humanity, easily observable extra-(Solar System) objects greatly helped understanding certain phenomena inside the Solar System. Importantly, the “precession of the equinox”, and also true periods of heliocentric orbits lying near the ecliptic.
Imagine a system like our Solar System with indigenous astronomers who are unaware of far-away objects (or cannot determine their bearings). How can astronomers possessing some Early Modern technology learn of absolute (inertial) spacial directions then? Ī̲ see several possibilities: looking at highly inclined subsystems (think Uranus with its rings and satellites), noticeably eccentric orbits (such as of Mercury or, occasionally, of comets), or just inclined orbits (think Pallas). But do other reliable references exist?


texts: Bright, brief light in sky this morning (daytime) - satellite flare?

texts:
This morning at 8:00am UK time, give or take about 3 minutes, I saw a very bright light in the sky which seemed to get a little brighter, lasting for maybe 5 seconds after I first noticed it, then faded out to nothing for a few seconds, then came back for another few seconds and disappeared entirely.

I was at around the following co-ordinates, and I was looking towards the South:

Lat: 51.980619 Long: -0.8443739614449441

I'd say it was at something like 30 degrees inclination but that's a really rough guess. It was somewhere around a third to half way between the horizon and overhead.

I know there are duplicate questions about this kind of thing BUT I believe this is different because:

I saw it during daylight. The sun was up, albeit behind clouds.
The light was VERY bright, when I first saw it I thought it was Venus but then it obviously faded out. I think it was probably even brighter than Venus would have been.
I have already ruled out Iridium flares by looking at Heavens Above. I have seen Iridium flares once or twice before and I think it looked similar.

Presumably there aren't too many objects in the sky that can get that bright. Are there any other objects which I could track apart from Iridium sats? Can anybody else find anything it might have been?


texts: If the universe keeps expanding, can we travel to the edge of the universe?

texts: If the universe keeps expanding, is it possible to travel to the edge of the universe?


texts: I see that there are a number of stars that have a number at the end of them. Ross 128 is an example. What does this number mean?


texts: Neutron stars and distribution of heavy elements

texts:
In the news, of course, is the theory that much of the mass of the heaviest elements in Earth would have come from colliding neutron stars.  This graphic gives one such analysis:

Origin of the Elements in the Solar System by Jennifer Johnson is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License. (Larger version at http://www.astronomy.ohio-state.edu/~jaj/nucleo/)

I don't know how accurate this is, but the URL looks good.  Also, this seems to be a new theory, and AFAIK this is the first actual evidence for it.

If this is correct, what are the implications for the quantity of heavy elements that would be found on planets outside our solar system?  In particular, I guess, the very heavy ones: gold, platinum, thorium, uranium...

We've been watching the skies for signs of neutron star collisions for several years now (IIUC), and I guess we're starting to get an idea of the frequency of this event.  And I've seen estimates of how much gold etc. was produced by this particular event.  How many planets would one such collision supply with the quantity of heavy elements in Earth?
(I guess we only really know about gold in the Earth's crust, and to some extent in the mantle; are these elements concentrated in the core?  Any idea about heavy elements in other planets of our solar system?)

So: given the frequency of the event per galaxy, the estimated number of stars with planets in a galaxy, etc., is it likely that most planets are deficient in heavy elements, as compared with Earth?

(Side comment: if so, then nuclear wars might be rare or impossible on those planets.)


texts: Is Diffraction of light observed in gravitational lensing/microlensing?

texts: As far as I understand the wave-optics effects,such e.g.diffraction at a caustic, are hardly observable in the gravitational lensing. Are there any observations where the diffraction paterns of the visible light have been seen? If not visible, which wavelength?


texts: Present distances between planet. How can I find them?

texts:
It's "commonly known" how distant are our solar system planets from Sun. But we can't easily say that about planets, which distances can differ greatly, without some observations (or simulations, knowing their state in some moment in time).

How can I can check 'actual' relative distances or positions of planets?


texts: How the position of this black hole known?

texts:
How do scientists know the positions of black holes?
Observe the highlighted area in the image:


texts: What percentage of visual stars are actually binary stars?

texts: I know this is such a thing as a binary star where for example two stars rotate around a central point of gravity but to the naked eye are just a star.  What I do not know is how common this is (approximately)?


texts:
An heliostat is a device capable of reflecting the sun in a fixed point while the sun itself moves into the sky, thanks to a moving mirror.
But this company astonished me with its invention: a static heliostat! Rather than mounting a mirror on a pan&tilt mechanism, they designed a curved mirror which, at any time in the day, reflects sun in a same point (actually same strip).
http://cleardomesolar.com/solareflexpanels.html

How can I design a static mirror which reflects a sun-strip over a wall all along a day? Let's suppose I have these data:

Wall exposed to North.
Mirror 5 meters away.
Apprximate location: 42N, 12E.

I am trying experimenting with Geogebra and OptGeo but with no luck so far.
I can reorient the mirror by hand every week or month, but I don't want to have to reorient it hour by hour!
Geogebra example:

https://www.geogebra.org/m/ukkrcv3c
Optgeo example:

Maybe Sunpath3d page can help:

http://andrewmarsh.com/apps/staging/sunpath3d.html
Also this page may be useful:
https://www.sunearthtools.com/dp/tools/pos_sun.php


texts: Is the passage of three asteroids near Earth today just coincidental?

texts:
I just saw in the advertisement-laden tabloid Express that three near-Earth astroids will pass the Earth today:

  The first of the three, dubbed Asteroid 2018 TU4, will come as close as 0.03637 astronomical units (au) or 14.16 lunar distances. around 3.13pm BST (2.13pm2 UTC)
  The next asteroid to pass the Earth is Asteroid SL3 at around 3.36pm BST (2.36pm BST).
  Lastly, Asteroid 2018 TS1 will come closest to Earth at around 3.45pm BST (2.45pm UTC) today.

Question: Is this just coincidental, or is there some relationship between these three particular asteroids, perhaps in the past, that would make their near-coincident arrival more likely?


texts: Is there work underway to push the long baseline capabilities of the Event Horizon Telescope to sub-millimeter wavelengths?

texts:
The Max Planck Institute for Radio Astronomy's press release Something is Lurking in the Heart of Quasar 3C 279; First Event Horizon Telescope Images of a Black-Hole Powered Jet shows a stunning montage of three Event Horizon telescope images at 7, 3 and 1.3 mm wavelengths (43, 86 and 230 GHz) demonstrating how the highest frequency in combination with the planet-sized baselines work together to produce observations at "an extreme 20 microarcsecond resolution", quoting the title of the April 5 2020 Astronomy and Astrophysics paper Kim et al. 2020 Event Horizon Telescope imaging of the archetypal blazar 3C 279 at an extreme 20 microarcsecond resolution.
From How does ALMA produce stable, mutually coherent ~THz local oscillators for all of their dishes? I know that ALMA's receivers can go as far as about 950 GHz. Is there work underway to increase the number of radiotelescope sites around the Earth with circa 1 THz receivers to push the long baseline capabilities of the Event Horizon Telescope to sub-millimeter wavelengths?


texts:
What is the inclination of Mercury's orbit w.r.t. the Sun's equatorial plane?
Additionally, what is the orientation of Mercury's orbit (long axis) w.r.t. the Milky Way?


texts: What uncertainty does an error bar signify in astronomy?

texts:
When an astronomer talks about her/his topic and shows an X/Y-plot with error bars. What should one assume that those error bars represent?
1 standard deviation? Or 2? Or some specific significance level like 95% or 99%?
Is there a generally understood convention for this, or does it vary depending on topic? I've noticed that it is very rarely explicitly stated what the meaning is of the range which the error bars cover.

And how are the cases treated, where exact observations reveal a variation in the actual population? Not "errors", but natural true certain variation. Are there other bars to illustrate that range of true values, as opposed to the variation due to observational uncertainty?


texts:
I know that the solar system is tilted 62.6° to the plane of the galaxy.  I'm curious whether this angle changes over time, and what are the extents and time frame of any such oscillations if they exist?

Upon reflection, I'm assuming that since such an oscillation would require a change in the overall angular momentum of the entire solar system, and that would necessitate a collective re-orientation of the orbit of every planet, dwarf planet, SSSB, etc. related to the Sun that it's unlikely that any such mechanism exists?


texts: Has the existence of earth-sized rogue planets been confirmed?

texts:
The list of known rogue planets provided by Wikipedia is fairly short. Some are "candidates"; others "may be" red dwarfs. The two confirmed rogue planets are several times the size of Jupiter.

I understand that rogue planets can only be detected if they glow (which immediately brings the phrase "red dwarf" to mind) or if they cross the path of light emanating from a star. This makes detection extremely difficult.

The reason I ask is I'm not quite certain whether objects the size of Jupiter or smaller can even exist in interstellar space. Maybe dark matter grinds them to dust, or maybe they implode in the absence of any meaningful inertial frame - I don't know. Has anything Earth-sized been detected out there?


texts:
I took an image of Jupiter through my 8" Dobsonian Telescope, attaching a DSLR and a 1.25" Barlow Lens where the eyepiece goes, as shown in this video: https://www.youtube.com/watch?v=reFxoF3XoaU

Through numerous online sources, I learnt that to find the angle of view of my image, the magnification of my image needed to be calculated, and that this value along with the given field view for my eyepiece.

http://www.rocketmime.com/astronomy/Telescope/Magnification.html:

The above website answers the following question, the calculations of which I attempted to mimic.

  My first telescope was a Meade 6600 -- they don't make it any more -- it's a 6-inch f/5 Newtonian scope. It came with a 25mm eyepiece. So... what was the magnification I was getting with this scope?

Here are the calculations I did in hopes of getting the above result:

$$\textrm{Diameter} = 8'' = 203.2\ \textrm{mm}$$

$$f_{\textrm{ratio}} = \frac{\textrm{focal length of objective}}{203.2\ \textrm{mm}}$$

$$\therefore \textrm{focal length of objective} = 203.2 \cdot 5.9 = 1200\ \textrm{mm}$$

$$\textrm{Magnification} = \frac{\textrm{focal length of objective}}{\textrm{focal length of eyepiece}} = \frac{1200}{x}$$

As shown in the video (the first link above), I didn't use an eyepiece to take my picture - I used a barlow lens, a couple of adapters, and a DSLR. So at this point, I am not sure what value to use for the "focal length of the eyepiece." How can I proceed to calculate the magnification?


texts: What is projected separation and how can I make sense of its unit (h^-1 kpc)?

texts:
I have been reading this paper on the separation of a binary quasar in which it states:

  At a projected separation of 8.3/h kpc (Omega_matter = 1), CTQ 839 would be the smallest projected separation binary quasar currently known.

What is meant by projected separation and where does this unit come from?


texts: Understanding energy loss in a telescope aperture due to atmospheric dispersion

texts:
I'm trying to understand energy losses due to atmospheric dispersion, given the plot below from the Keck telescope.
For a typical seeing I'm told that there's 80% encircled energy in 1". The aperture of the instrument is 2". The plot shows the dispersion as a function of zenith distance for different wavelengths.
What is the maximum zenith distance with < 20% loss at 3200 angstrom due to atmospheric dispersion?
I'm not used to thinking about aperture in arcseconds, but I suppose it's bigger than the seeing, usually? Also, the fact that 80% of the energy is encircled in 1", does that imply that you catch 100% with an aperture of 2" or am I overlooking things?
I don't really know how to use this plot. At a certain fixed zenith distance, if for example the y-value is -3, does that mean the seeing increases with 3" (e.g. if seeing was 1" without dispersion, would it be 4" with dispersion)? Or does it not make sense to think about seeing "without" atmospheric dispersion?


texts: Why don't they make an image of the black hole in the M33 galaxy?

texts: Since we see the Triangulum galaxy M33 from a quite vertical position (contrary to our Milky Way and a bit the Andromeda galaxy) it should be easy to image the black hole in the center of it, shouldn't it? Why did they prefer to first image the black hole in a galaxy which is about 20 times farther and thus harder to photograph the black hole in its center?


texts: Where did the nickel in the Earth's core come from?

texts: Why is there nickel in the core of the earth? Does it come from collisions of two neutron stars? And how did we know the core of our planet is made of nickel-iron alloy? Thank you.


texts: A very basic question, but one to which I keep finding different answers: does Mercury have a liquid core, or is it all solid? Whatever the reason, what are the causes of it being so?


texts:
The Milky Way has a bright center we can't see directly because of space dust. Are there's regions of the galaxy free of that dust that could receive all that light and radiation, right? Would it be possible to exist an 'ecosphere' around the galaxy's center where planets receive as much energy from it as the Earth receive from the Sun? Would it be possible to rogue planets orbiting the galaxy's center at that distance to sustain life?

Or it's the case that interstelar dust always blocks most energy? Even in a 'polar orbit' around the galaxy's center?

If so, how many of them could exist? More than planets orbiting stars?


texts: How to find the local azimuth of the highest point of the ecliptic

texts:
I would like to use pyephem or skyfield1 to find the degree of the local horizon (starting from South = 0°) at which is located the highest point of the ecliptic.
Note that I am not trying to find the culmination of a planet. It could well be that, when looking South, there is no planet on the ecliptic by that time/latitude, but there will still be a highest point of the ecliptic. Can anyone help?
1Skyfield is preferred over PyEphem for new projects for several reasons


texts: If nothing can pass the schwarzschild radius, how can black holes even start?

texts:
From our point of view, no object can fall into a black hole in finite time. The object will seem to be more and more red-shifted to us, but it will never quite pass the schwarzschild-radius / event horizon. (Of course the time frame of the falling object is another thing, but we are well away from any direct effects of black holes on us)

Having said that, how can black holes come to existence? As soon as there would be a schwarzschild radius, nothing can cross it. To me this seems like a chicken-and-egg problem, so no black holes can possibly exist.

Obviously the black holes in our universe do not seem to be aware of this, so what am I missing?

Thanks in advance :-)


texts: How would I code to find the seeing of a binary star system in python?

texts: I have fit images of binary systems and want a program that will help determine which ones are highest quality, the seeing. The simplest way is apparently to equate it to the FWHM of the Gaussian of the point spread function of one of the stars. But I'm at a loss as to how to do this. I've searched for any helpful tutorials online but can't find an understandable method.


texts: Luminosities and Apparent Brightness of Two Stars of which one is 8 times the distance of the first star

texts: Suppose two stars have the same apparent brightness, but one star is 8 times further away than the other. What is the ratio of their luminosities? Which one is more luminous, the closer or the further star?


texts:
There is a phrase in a Science Daily article which appears to be wrong:

The Milky Way has a very high content of carbonaceous dust, which has been shown to be very rare in other galaxies.

Is there a theory that explains these observations?


texts: How much helium has been created since the Big Bang?

texts:
When I try to find figures for the amount of helium today and just after the Big Bang, I get similar figures.  I was expecting that all of the stars since then would have created more helium.  Is the amount below our ability to estimate?  Is helium being consumed at a similar or greater rate to produce heavier elements?

Alternatively, can we measure/ estimate a drop in the hydrogen?  I presume that little hydrogen is being created.  I am unaware of any common nuclear process which creates lone protons.  (Please correct me if appropriate.)

Clarification: The Wikipedia Big Bang article mentions helium being created after a few minutes in the Big Bang nucleosynthesis.  So, it is helium created after this point that I am asking about.  I am presuming that negligible helium was created between this point and the first stars much later.  (Again, please correct me if I am wrong.)


texts:
Today the NY Times published an article that explained how to see NEOWISE at night.
The article explains it like this:

To catch NEOWISE yourself, look up at the northwest skies about an hour and a half after sunset. Experts suggest going to the darkest area you can for best viewing. Find the Big Dipper and follow its ladle as it arcs in the direction of the horizon.

NEOWISE will appear under the Big Dipper about 10 degrees above the horizon and be about as bright as that constellation’s stars. If you hold out your arm, 10 degrees is roughly the part of the sky covered by your fist. Over the next few days, NEOWISE will move higher in the sky and be easier to spot, reaching its apex on July 23, when it makes its closest approach to Earth.

It says that I'll be able to see the comet "under the Big Dipper about 10 degrees above the horizon".
What "horizon" is the article referring to? It says above the horizon and under the Big Dipper. Is the Big Dipper just above where the sun disappears and the comet will be seen in that area?


texts: Could dark matter be "inside-out" reality?

texts:
Where we are, and in the conventional galaxies etc. that we see, there is a whole lot of relatively uniform space but in isolated places within that space, there are pockets of concentrated "mass" which is highly organised into all the objects we observe and study, and out of which we are made.

Now suppose that there were regions of space where that is all turned on its head, and there were huge vast swathes of relatively uniform matter, and within that matter there are pockets of "space" which is highly organised into some other form of object, out of which other objects and beings are made.

Obviously on the first, and simplest test - the question of "how much" dark matter there is, this theory passes the empirical test of reality with flying colours, i.e. astronomers seem to observe much more mass in the regions of hypothesised dark matter in accordance with what this conjecture implies.

What other testable predictions does this conjecture make, and how well do they fit our observations?


texts: How would Aurora look like if no magnetic field was there to protect the Earth?

texts:
The greatest part of the Earth is protected from the Solar wind by its magnetic field. This field makes the wind particles (mainly protons and electrons) the beauty of Aurora appear.
Suppose the magnetic field wasn't present. The Solar wind particles hitting the southern and northern parts of our planet would distribute themselves over whole the Earth's surface.
How would Aurora look like?
For certain it would be not slowly swirling (following the slowly changing magnetic field lines). Will we see a sparkling sky? Or what?


texts:
I was wondering if anyone knew of any resources to understand the linear limb darkening coefficient, $u$. That is to say, how the $\theta$-dependent coefficient $u$ (or sometimes $b_{\nu}$) varies with wavelength and with stellar effective temperature.

I've looked at a number of sources, such as Schwarzschild (1906), Milne (1921) and my own lecture notes and others, but nothing on this coefficient? Does anyone know where to even start looking for information of the properties of $u$?


texts: Why temperature of dark side of moon is not 3 Kelvin

texts:
The temperature of the space between Earth and the Moon is around 3 Kelvin ($\approx -270^\circ {\rm C}$). The moon has no atmosphere, therefore the heat convection is not possible from the bright side to the dark side on Moon.
Now, if the temperature of the space around the moon is $3 {\rm K}$, then how the dark side of the moon is having a temperature of $100 {\rm K}$?
References

https://sciencing.com/temperatures-outer-space-around-earth-20254.html
https://www.space.com/14725-moon-temperature-lunar-days-night.html


texts: I am not quite sure if it would, considering i'v looked through countless websites and found nothing and would like to know if it could clear its path and join the other planets?


texts: Could asteroid 'Oumuamua actually be round?

texts:
News articles have mentioned that the recently discovered asteroid 'Oumuamua is theorized to be greatly elongated based on observations of brightness variation. However, this hypothesis seems to be based on the assumption that the object's albedo distribution is reasonably uniform.
What if it isn't? Could large periodic brightness variations also be explained by 'Oomuamua having two highly contrasting hemispheres like Iapetus? If the astronomers involved have already eliminated this competing explanation, how would they have done so and with what additional observational data?


texts: How fast do the poles of Jupiter and Saturn precess?

texts: As Jupiter and Saturn have very fast rotation periods, about 10 and 11 hours, respectively, I am assuming that their poles will precess much faster then Earth. Since Earth's poles precess every 26000 years, I think Jupiter and Saturn would have a precession time of about ~10000 years or so. Is this estimate correct or am I way off?


texts: Is the centre of axial precession perfectly perpendicular to the ecliptic?

texts:
It is my understanding that the Earth's axial precession is such that the direction of the North pole pointing to the celestial sphere traces out a circle with a period of roughly 26,000 years. My first question on reading this was, where is the centre of that circle? In other words, what axis is the Earth precessing about? I had assumed this would be somewhat arbitrary but have since learned that it points towards the north ecliptic pole. Am I then correct to assume that planets naturally tend to rotate in the same plane as their orbits, but the effects of precession caused by other massive bodies cause the axis of rotation to oscillate around the north ecliptic instead?

If so, then what is going on with Uranus and it's unusually high axial tilt? Is this another phenomenon or does Uranus' rotation axis also precess about it's own ecliptic north pole? Albeit with a much larger amplitude.


texts: General relativity is often explained as saying spacetime is curved by gravity, what does this mean? How could we perceive a curve in spacetime when there is no external "straight" reference frame for instance?


texts: Do gravitationally bound (e.g. orbiting) objects really resist the expansion of space?

texts:
Thinking about the expansion of space, it is commonly explained that gravitationally bound objects (like galaxies and galaxy clusters) will not be affected by the expansion of space (dark energy).  I personally don't get why this would be, I would think galaxies, and things orbiting one another (e.g. solar systems) would be impacted.  If space doubled, the orbit distance should double.  I do get that things bound together gravitationally (perhaps a second definition / originally meant definition of "gravitationally bound") (e.g. planets, stars, asteroids, etc...) would not get ripped apart as space gradually doubles.  They would just pull themselves back together, and resist the very weak force of the expansion of space.  Is my understanding correct that things held together by gravity (like stars and planets) will hold together as space continues to expand, but things in orbit (e.g. stars orbiting within the galaxy, and planets orbiting stars) will be moved further out with the expansion of space?  It seems this could be fairly easily verified or refuted by seeing if ancient galaxies (those really far away) are denser than closer galaxies.  If they are denser, then this is strong support for the idea, and if not, then it largely refutes it.

I have a feeling this might be why quasars stopped happening at some point, and are now just observable in great distances (where we are seeing them in the past).  My understanding is that a quasar is the supermassive black hole at the center of a galaxy feeding on large amounts of material.  Back to my main question though, does the expansion of space thin out galaxies / solar systems?


texts: How accurately can you tell the time using a photo of the stars?

texts:
If I were to go out on a clear night, in an area with low light pollution, and take a photo of the stars, could an expert analyze the photo and figure out what date the photo is from? We can assume a powerful camera, but not reaching up to the strength of a telescope.

This question stems from a larger project. It would be very convenient for me if it were possible to take a photo of the stars to tell the time. Even more convenient if you could narrow it down to within 10 minutes, but if that's not possible I'm wondering how close we can get. Can you tell the year? The millennium? Do you need to know which location on Earth the photo was taken from? Does it help if you already know the year in which the photo was taken?

You can assume access to modern computing, existing databases, state-of-the-art software, etc. (no supercomputers)

Thanks!


texts: I am a layman in astronomy. Can someone please explain it to me whether the M-theory can be used to explain what is happening in the centre of the black hole where the singularity exists? Or is it still necessary to peek inside a black hole to gain that information?


texts: Is Jupiter really shepherding the main belt, and Neptune the Kuiper belt?

texts:
By "dominating another object's orbit" my understanding is that the most massive body's gravity has so much influence that, when they come close, it makes the other body/bodies' orbits shift or change, either certain parameters (such as apoapsis, periapsis, inclination etc.) or up to pulling it completely out of its current orbit (thereby perhaps ejecting the body from it or making the body collide with the dominating body or a satellite of the dominating body). However, as far as I can determine, Jupiter is unable to alter the orbit of Ceres; both of them are in stable orbits, nor can any other of the main belt's equilibrium-shaped object's orbits (Interamnia, Hygiea, Pallas and Vesta) ever influence themselves to the point that one's orbital parameters are altered nor does Jupiter exert enough gravitational influence on any equilibrium-shaped main belt object to alter its orbit.
The same seems to be true for the Kuiper belt: For every two complete orbits made by Pluto, Neptune makes exactly three orbits. So both object's orbits are stable and Neptune doesn't influence Pluto's orbit in a way that it would be altered, nor is any other spherical TNO's orbit manipulated either by Neptune or by themselves between each other.
Am I right and is there even any equilibrium-shaped object directly orbiting the Sun that ever altered another equilibrium-shaped object's orbit in recorded history, or would be able to do so in a close approach? As I see it, all ellipsoidal objects orbiting the Sun in our system are on stable orbits that won't change unless some interstellar 'visitor' might meddle any up.


texts: Could not slow neutrinos orbit galaxies and clusters, thus comprising a large component of even COLD dark matter?

texts:
Cold dark matter is the type of dark matter that is most eminently neutrino-free. But neutrinos themselves suffer a large survivorship detection bias (“all the neutrinos you can detect necessarily have to have relativistic speeds”) https://physics.stackexchange.com/questions/267035/where-are-all-the-slow-neutrinos
By the same principle that there are more pebbles than boulders, and more red dwarfs than blue giants, slow neutrinos should be more abundant than the fast, detectable ones.
Non-relativistic (slow) neutrinos - in particular those going at below the galactic escape velocity - could be a major competent of cold dark matter: slow neutrinos could be slow enough to orbit galaxies and galactic clusters and thus form a significant amount of cdm, which should be shaped as a galactic halo.
If neutrinos are produced at all speeds, those stellar (modern) neutrinos below galactic escape velocity will accumulate indefinitely. This should generate a halo-shaped cloud, and this could comprise a large part (of course 15% are MACHOs etc https://ned.ipac.caltech.edu/level5/Sept17/Freese/Freese4.html - I am assuming here a multi-component DM) of cold dark matter.


texts: Can we hear something on Venus, Mars and Titan?

texts:
Mars, Venus and Titan have an atmosphere and we can theoretically step on them (and die quickly).

So, as an example, let's say we can survive on these objects without a space suit. I say: “Hi” on any of these objects. Would I hear what I said or not?


texts:
I don't know ANYTHING about astronomy but I know what I saw and 2 of my siblings saw it too. I initially thought it was a shooting star, but a Google search quickly made it clear that it wasn't.
it was of similar brightness to the surrounding stars and weirdly wasn't moving in a single direction. it was moving erratically in no particular path, was not constrained to a specific area and almost mimicked what a laser point would look like if a human was moving it randomly. I do not believe satellites move at the speed at which it was moving and as randomly..
what could this possibly be?


texts: Halley's Comet current location in sky and visibility?

texts: I am an amateur in astronomy, but recently I wonder if it is possible to see (in a photo, maybe, if not in a telescope) Halley's Comet when its not close to earth. If there is such photo, how I can find it. Thanks in advance.


texts:
I have been trying to create a graph which shows the distances between the stars and the earth, yet I could not obtain the desired graph as seen below (click to zoom in):

My graph:

As @uhoh suggested, I overlaid one graph on top of the other.

I apologize for posting this confusing graph

The combined graph denotes that the positions of the curves in my graph totally differ from those in the expected graph.

I followed this guide to calculate the position functions of the stars.

My Question: Did I made any mistakes that resulted in the anomalies?

Thanks in advance.

Annotations for the Code:

Name - Name of the star
RA - Right Ascension in degrees, ICRS coord. (J2000)
Dec - Declination in degrees, ICRS coord. (J2000)
pm_mRA - Proper motion in right ascension, in miliarcseconds per year
pm_mdec - Proper motion in declination, in miliarcseconds per year
vr - radial velocity in kilometers per second, a positive value means that the star is moving away from us
mparallax - parallax of the star in miliarcseconds
d - distance between the star and the earth

My Code:

def parseTextFile(file_name, delimiter=",", header=0):
    """ Parse a text file to a list. The file contents are delimited and have a header. """

    with open(file_name) as f:

        # Skip the header
        for i in range(header):
            next(f)

        data = []

        # Parse file contents
        for line in f:

            # Remove the newline char
            line = line.replace('\n', '').replace('\r', '')

            # Split the line by the delimiter
            line = line.split(delimiter)

            # Strip whitespaces from individual entries in the line
            for i, entry in enumerate(line):
                line[i] = entry.strip()

            # Add the contents of the line to the data list
            data.append(line)

        return data

fig = plt.figure()
ax = fig.add_subplot()

#time span
time = np.arange(-60000,100000,10)
count = 1

xdic = {}
ydic = {}
zdic = {}

#multiple lines of data
for star in parseTextFile(file_name, header=1):

    name = str(star[0])
    RA = float(star[1])
    Dec = float(star[2])
    pm_mRA = float(star[3])
    pm_mDec = float(star[4])
    vr = float(star[5])
    mparallax = float(star[6])

    pm_RA = pm_mRA * 0.001
    pm_Dec = pm_mDec * 0.001
    d = 1 / (mparallax * 0.001)

    #Transverse velocities
    vta = pm_RA * d * 4.740
    vtd = pm_Dec * d * 4.740

    #Linear velocities
    vx = vr * np.cos(Dec) * np.cos(RA) - vta * np.sin(RA) - vtd * np.sin(Dec) * np.cos(RA)
    vy = vr * np.cos(Dec) * np.sin(RA) + vta * np.cos(RA) - vtd * np.sin(Dec) * np.sin(RA)
    vz = vr * np.sin(Dec) + vtd * np.cos(Dec)

    #unit conversion from km/s to pc/year
    vx_pcyr = vx / 977780
    vy_pcyr = vy / 977780
    vz_pcyr = vz / 977780

    #initial positions
    xi = d * np.cos(Dec) * np.cos(RA)
    yi = d * np.cos(Dec) * np.sin(RA)
    zi = d * np.sin(Dec)

    #position functions
    x = xi + vx_pcyr * time
    y = yi + vy_pcyr * time
    z = zi + vz_pcyr * time

    distance = np.sqrt(x ** 2 + y ** 2 + z ** 2)

    ax.plot(time,distance,label=name)

ax.set_xlabel('Time (Year)')
ax.set_ylabel('Distance (pc)')
ax.legend()
plt.show()


texts: Why both sunrise and sunset use the position of the sun's upper limb?

texts:
It is my understanding, that astronomical moments of both rise and set use the relative position of background object's upper limb to the foreground object's horizon.
When were these definitions formulated?
Is this done purely because sunrise and sunset are the main examples of such events and it is easier for the naked eye to tell when sun is completely below horizon?
Wouldn't this offset the symmetry of rotations (since the "day" is always longer than the "night" by the duration it takes the background object to move fully below the foreground horizon)?


texts: Understanding the theory of an expanding Universe

texts:
How did Edwin Hubble determine the Universe was expanding?

Was he looking in a particular direction?

And where does this Galaxy sit in the expansion.


texts: In which direction does the ecliptic plane make an angle of 60 degrees with galactic plane? Is it toward the galactic center? (It can have any 360 degree orientation.)


texts: What would be the outcome for life in our galaxy if the merger of the Milky Way and Andromeda creates a Quasar?

texts:
If predictions are correct, the Milky Way and Andromeda are set to collide in around 4 billion years. If, when this occurs, a Quasar is formed by matter being accreted to the common galactic center (perhaps with the two supermassive black holes forming a binary), what would be the outcome for life in the new galaxy?

It's known that galactic collisions were much more common in the early universe; most Quasars are observed at high redshifts. It isn't clear if there are other conditions necessary to produce a quasar other than just the galactic collision itself, so obviously this is just speculation, but it is clear that Quasars are some of the most energetic systems in the Universe; if one were ignited so close to home, would every trace of life in the galaxy go out in a blaze of glory?


texts: I know light and sound travel along wavelengths and in all diagrams I have seen the pictures of photons travelling up and down and forward. How does something travelling so fast stay within the confines of the wave please ? I am new to this site but intelligent enough to understand complex answers.


texts: Is there a luminosity class for brown dwarfs?

texts: I've been reading about brown dwarfs, and checking their spectral types, and I noticed that they do not have a luminosity class (V, VI, etc). So I am wondering, do brown dwarfs have a luminosity class, or is it intentionally absent, or is it defaultly V or VI?


texts: Plot of best available resolution vs wavelength - radio through gamma rays?

texts:
What I'm looking for is a graphic that shows in a general way the best available telescope resolution vs wavelength throughout the entire wavelength spectrum. So for example, there might be two very high resolution peaks aroud

millimeter wavelengths (ALMA)
visible wavelengths (HST and many ground telescopes with Adaptive Optics)

The beautiful image below from this great answer got me thinking. I have reposted it from there.

  Image courtesy of Wikipedia user Hunster under the Creative Commons Attribution-Share Alike 3.0 Unported license.

  The infrared, ultraviolet, and x-ray images come from the Spitzer Space Telescope, the SWIFT observatory, and the Chandra observatory, respectively.


texts: What's the closest Venus gets to the moon?

texts:
I recently observed the beautiful sight of Venus quite close to the crescent moon, and was wondering, what the closest (angular distance as seen from earth) they come.

Are there on-line tables or calculators for finding when such nearest events occur and are visible?


texts:
I've often come across sun path charts like this (Wikimedia Commons) that show the position of the sun at any point of the year, at any time of day, for a specific location (or a set of locations), on an azimuth-elevation polar plot:

I'd like to get the exact same chart (or data, to create my own chart) for any given star, such as Aldebaran or Sirius, for a given point on Earth.

I'm looking into Stellarium scripting, as well as the HYG stellar database (I am not familiar with the mathematics of right ascension and declination, or how to convert this to azimuth-elevation like in the example). Is this a very unusual data product to ask for?


texts: What if a moon like triton or a frozen extraterrestrial body containing lots of frozen ice were set on a collision course with Venus.  Would an inlfux of huge amounts of H2O precipitate a possible terraforming of venus in such a case?


texts: If we find asteroid flying towards us, can we change it's direction with white painting? Will the ray from sun do something?


texts: Could a habitable satellite of a gas giant have a stable subsatellite?

texts:
I have set a science fiction story on a moon, orbiting a gas giant (which orbits its star at approximately the same orbit as the Earth around the Sun), and given this moon its own satellites.  The moon is Earth-sized, and the moon’s satellites are on the order of a large asteroid each (perhaps up to half the size of the Moon … Luna if there was any confusion with the number of times I said ‘moon’ in this post.)

I am a computer nerd, not an astronomer, so I’m wondering if this is something that is at least possible?  Could the orbits of the gas giant around the star, the moon around the gas giant, and the subsatellites around the moon remain stable for the requisite billion or so years for life to develop on the moon?  Could the moon be habitable?


texts: What does "additive fringing from the (multiplicative) twilights" mean?

texts:
The question How can I make the fringing pattern visible in my flat (twilight) images for filter i? includes:

  I have a bunch of twilight flats that have been preprocessed (dark, bias, overscan etc.) and need to remove the additive fringing from the (multiplicative) twilights. I normalized each one by dividing by the mean and then combined them using ccdproc in astropy. I then divided the normalized flats by this "new" flat and viewed them in DS9 but I still cannot see the fringing.

and the OP went on to post an answer where fringes are visible.

But I haven't any idea what causes "additive fringing" (which I assume means it's a fringing pattern that is additive to an otherwise corrected image) nor what "multiplicative twilights" means.

Could someone explain the basics behind both?


texts: First time visit to dark sky stargazing site: what do I need?

texts: Complete newbie here. I have an opportunity to visit one of the few designated dark sky sites here in Pennsylvania, Cherry Springs State Park. I plan on camping out over night, but I have never gone stargazing before, don't use a telescope, and I don't know what the protocols are as far as binoculars? glasses? Etc. for viewing the night skies. The park allows no lights, save for flashlights covered with red tint. Is there anything else that you more experienced astronomers would suggst that I need to have with me? What should I bring? What should I expect for my first observation tour ever? Thank you.


texts: Would bagging an asteroid destroy valuable science about it?

texts:
NASA has a plan called "Asteroid Redirect Mission option A". It would robotically put an asteroid of a few meters diameter in a bag and push it into reach of astronauts for thorough examination. 44 tonnes of meteorites falls on Earth every day and almost 50,000 meteorites have been found on Earth. So the unique advantage of capturing a pristine asteroid, however tiny, is that it will not have been deformed by entering Earth's atmosphere. It might be a rubble pile and/or its surface might be covered by regolith or maybe even volatiles since it might have formed and always existed in microgravity. Even the Moon is covered by hoovering electrically charged dust near above its surface, ionized by cosmic or Solar radiation. And surface properties are important because it is only the surface which can be observed by telescopes and Earth based radar.

But wouldn't bagging and pushing an asteroid destroy such delicate surface and rubble pile properties?


texts: What if a white dwarf is less massive than her partner?

texts: For example: a system with a 0.2 solar mass white dwarf orbiting a 0.25 solar mass red dwarf. Does the red dwarf steals mass from the white dwarf or vice versa.


texts: Can a star fall in a super massive black hole without getting destroyed?

texts: This is the first of many similar questions I have to build up to a specific question or scenario that I want to explore and find an answer to.


texts: The drift of the Moon's equatorial rotation velocity

texts:
Are there any citation or documentation showing the measured degradation of the Moon's equatorial rotation velocity (thus affecting its moon's axial rotation)?

I am looking for the drift of the Moon's axis rotational speed, presumably over 10,000 years or more.


texts:
I want to simulate the orbits of the planets from our solar system. I want to use orbital elements to calculate the current position(xyz) at a time t. The simulation doesn't have to be too exact, but the initial position of the bodies should be somewhat realistic.

Doing some research on the calculation I stumbled upon the following formula:

R,X,Y,Z-Heliocentric Distances
TA - True Anomaly
N - Longitude of the Ascending Node
w - Argument of the Perihelion

R = a * (1 - e ^ 2) / (1 + e * Cos(TA))
X = R * (Cos(N) * Cos(TA + w) - Sin(N) * Sin(TA+w)*Cos(i)
Y = R * (Sin(N) * Cos(TA+w) + Cos(N) * Sin(TA+w)) * Cos(i))
Z = R * Sin(TA+w) * Sin(i)

Source: https://www.physicsforums.com/threads/calculating-elliptic-orbits-in-cartesian-coordinates.712979/

For testing purposes I calculated the true anomaly with the help of the following calculator: http://www.jgiesen.de/kepler/kepler.html
It needs the mean anomaly and eccentricity which I took from Wikipedia. Doing some more research on the mean anomaly, I now believe that the time at which I want the position will be somehow fed into the calculation of the mean anomaly along with the time of the initial position.

Can somebody clarify for me on how to correctly calculate the position at time t with the above or a different formula. With the above formula I also think I need the initial values at a specific time.

I also want to say that I am not an astronomer and I don't have a clue on how to handle the calculation or which formula to use. The result of the calculations should mimic our solar system as closely as possible.

Thanks,
Rene Hollander


texts:
Recently I looked into the hottest(and coldest, but in another question) natural places. I find this to be a "cloud of searing gas that is surrounding a swarm of galaxies clustered together five billion light-years away in the constellation of Virgo". This place has a temperature of 300 million degrees Celsius, which is super hot even compared to the temperature at our Sun's core. A quick search why gives:

  A group of galaxies collided violently with another swarm of galaxies at a speed of 2,500 miles per second.

    https://www.skymania.com/wp/hottest-spot-in-universe-found/

However, what mechanism exactly causes this temperature? Friction? Or something else? Would stars there be fusing stuff from the outside?


texts: I'm curious about the difference between low redshift and high redshift universe. Is there any defined limit of redshift beyond which we call things high redshifted?


texts: Milky Way stellar number density : is the stated equation in this paper incorrect?

texts:
The paper is :
http://www.astro.washington.edu/users/ivezic/Publications/tomographyI.pdf

The equation is equation #23 in the paper. It's a model for the density of stars in the Milky Way's disk. It has an exponential dependence on both $R$ and $Z$. $R$ is the distance from the center of the galaxy, and $Z$ is the distance above/below the plane of the disk.

The relation is roughly this:

$$\varrho=\text{constant}\times e^{-\frac{R}{L}-\frac{Z+Z_0}{H}}$$

The problem I'm seeing is the $Z$-dependence of the formula. $R$ and $Z$ here are standard cylindrical coordinates. Thus, $Z$ can be positive or negative. The problem is that the formula blows up when $Z$ is negative. This is unphysical, since the number density must generally decrease going further away from the disk.

Am I missing something? Or should the equation really have an absolute magnitude of $|Z + Z_0|$?

[Added Later:]
I finished making a 3D demo of the stellar number density of the Milky Way. Note that your browser needs to support WebGL.


texts:
This question is inspired by, but different from, What happens if an ice cube is left in space?

Mark's accepted answer says "…if you stick your ice cube out in the Oort Cloud, it'll grow: the mean surface temperature is 40K or below,…".

To which the obvious response is Everything has a vapour pressure, so everything in the vacuum of space will evaporate eventually. Accordingly I thought it might be worth investigating why ice grains do exist. For which we need some numbers.

Vapour pressure of water at 40K

Most charts do not go that low. The best figure I have come up with was by looking at the pictures in Water Ice Films in Cryogenic Vacuum Chambers, a doctoral thesis by Jesse Michael Labello. Figure 4 on page 4 has graphs which, extrapolated by guesswork, suggest that the vapour pressure of water at 40K is less than $10^{-26}$ torr.

Atmospheric pressure in space

The Moon's atmospheric pressure is said to be $10^{-11}$ torr, and the New World Encyclopedia says interstellar space is $10^{-16}$ torr, and some answers on Physics Stack Exchange suggest about $10^{-25}$ for intergalactic space.

It appears, therefore, that ice grains at 40K do not evaporate because their vapour pressure is not high enough. Does it follow, therefore:

That ice grains would evaporate, even at 40K, if they were in a vacuum?
That, if the ice is at equilibrium with its vapour, the relative humidity of interstellar space is 100%? Or is the process of evaporation/condensation kinetically so slow that the universe is too young for it to have reached equilibrium?


texts: How frequently do Jupiter & Regulus have triple conjunctions?

texts:
I am wanting to know if the triple conjunction of Jupiter with Regulus in:
Sep 10, 3 BC
Feb 7, 3 BC &
May 8, 2 BC
with Jupiter later having a conjunction with Venus in Jun 17, 2 BC has happened since, and if so, how often does this triple conjunction happens?


texts:
It is often said that the Moon doesn't have an atmosphere. But there is an envelope of gas surrounding the Moon, albeit a thin one, so the Moon has at least an exosphere.
The Moon doesn't have its own magnetic field and has comparatively low gravity, so any atmosphere should be rapidly stripped away by solar winds and thermal escape. For there to still be an atmosphere, there must be some mechanism that that replenishes it.
What replenishes the lunar atmosphere, to compensate for loss from solar winds and thermal escape?


texts: Is there any way to find out what sky surveys are *currently active?*

texts:
I've asked a question about active sky surveys that might intercept a 2% of 4π patch of sky in the next six months and potentially record this dim (+22 to +26 magnitude) object.

I've added a bounty with about one more day on the grace period, the only thing helpful was a comment that suggested I ask for a "database of surveys".

Are there any pages that list at least major active surveys? That would be a start at least.


texts: Are the Leonid meteor storms a thing of the past?

texts: According to the Wikipedia article on the Leonids, "a close encounter with Jupiter is expected to perturb the comet's path, and many streams, making storms of historic magnitude unlikely for many decades". Does this mean there will not be another incidence of the famous storms which spawned thousands or tens of thousands of meteors per hour within our lifetimes? Or will the 33 year periodicity reestablish itself?


texts: When will all other galaxies become not visible from Earth/Milky way?

texts:
I know that because of the universe expansion, at some point we will not see any other galaxies from Earth, and we will be able to see only our own galaxy.
Does anyone have an origin or time estimation when will it happen?


texts: Can an SMBH recycle dark matter into energy?

texts:
I just had a conceptual question, hopefully it makes for some really interesting answers.

I was wondering, as most galaxies have an SMBH at their centre (see Kormandy & Richstone 1995; Richstone et al. 1998), could dark matter accrete onto the SMBH over time (perhaps perturbed by a galaxy collision, interaction or merger) and then recycle this matter as energy? Can dark matter help an SMBH grow?


texts: Measured values of the solar irradiance at other values than 1 AU?

texts:
It is straight forward to estimate the total solar irradiance of a planet using the Earth's solar constant, and scaling it according to the (mean) distance of the planets. But for which planets have measurements been made? A quick search of the usual suspects like arxiv.org or scholar.google.com did not yield any conclusive or easy to interpret results.

Mercury: $12\,121 {\rm W}/{\rm m}^2$ according to Wolframalpha which use the simple scaling. However, there are other sources, one of which claiming to cite a reference handbook's value of $9\,937 {\rm W}/{\rm m}^2$ which is a rather large deviation.
Venus: $2\,601.3 {\rm W}/{\rm m}^2$, according to NASA's Venus fact sheet, which is reasonable close to $2\,569 {\rm W}/{\rm m}^2$ according to Wolframalpha
Earth: $1\,361^{+1}_{-0} {\rm W}/{\rm m}^2$ according to Wikipedia on the solar constant
Mars: around $560.7 {\rm W}/{\rm m}^2$, this is probably measured more exactly
Jupiter: probably around $52.7 {\rm W}/{\rm m}^2$

How accurate are the values? What are the error bars?


texts: Is Mars visible from naked-eye from Michigan (47N, 88W) these days?

texts:
Is Mars visible at night sky of Michigan these days?

I was trying to search for Mars from Michigan (at elevation of 30 deg and azimuth of 220 deg) around 11:45 PM with binoculars of 20x60 but didn't get successful.


texts: Will there be public access to the New Horizons data from Ultima Thule?

texts:
I imagine New Horizons data from its encounter with Ultima Thule (2014 MU69) has started arriving.

Does anyone know if this data is public?

And, if so, how you can access it?


texts:
If I understand the principle of operation of operation of LIGO, it detects relative distortions of the two perpendicular arms. So if both arms are distorted the same way, nothing would be spotted.

In particular, any wave coming in the direction 45 degrees between the arms (both ways), or from above or from below - or generally any direction in the symmetry plane 45 degrees to the arms - would be completely invisible, and anything close to it would be very muted as the relative distortion would be minimal.

Is that correct?


texts: Mars vs Venus: the retention of atmospheres in relationship to Earth

texts:
Correct me if I'm wrong, but the factors than enable a planet to retain or lose an atmosphere seem to be: 1. Magnetic Field, 2. Solar Winds, 3.Weight of Gases, 4. Planetary Temperatures. 5. Distance from the Sun In regards to solar winds and planetary temperatures.

A strong magnetic field usually helps to retain all the gases, even the lightest as on Earth.  The magnetic field prevents solar winds and radiation from reaching the atmosphere and exciting the gases enough to escape the gravitation planet.
The Strength of the Solar Winds have the ability to excite gas molecules enough to escape the gravity of the planet. Their strength is determined by the planets proximity to the Sun. Their effects are mitigated by the strength of the magnetic fields and molecular weight of the different gases.
Molecular Weight of the Gases and the gravity of the planet. While Venus has a much stronger solar wind than Mars and almost no magnetic fields, it's not a question of maintaining an atmosphere, as much as maintaining what kind of atmosphere.  The lighter gases like Hydrogen, Oxygen and Nitrogen are not present on Venus, but CO2 and heavier gases are.  The heavier gases are much less easily excited due to their heavier molecular weight and thus remain, unable to escape the gravity of the planet.  That is not to say that the heavier gases aren't aren't blown away to one degree or another, but aren't blown away in more significant amounts.  Thus Venus has an atmosphere of these gases.
Planetary Temperature as well as the lack of a molecular field has a great deal to do with the lack of an atmosphere on Mars.  The lighter gases still escape but the heavier ones, more specifically CO2, remain, but mostly in frozen form.  The lower temperatures are also thought to be responsible for some remaining water, stored in the form of ice below the surface.
Distance from the sun determines the strength of the solar winds and planetary temperature.

From what I see, these factors, interacting, determine the ability of the planets to retain an atmosphere, and of course, what kind of atmosphere.  While my writing may have some issues, I'm not so much concerned with that this point(I can work on it), as I am to know if I have an accurate and comprehensive understanding of all the known factors that determine a planets atmosphere.  Thank you.


texts: What is the cost and benefit of building two identical telescopes?

texts:
I suppose that (especially space) telescope costs is dominated by design and development, not by material and manufacturing. So once a telescope has been developed and designed, how much extra would it cost to build a second copy of it? It seems as if spy satellites are built in batches of similar designs.

Would the science value of a second similar telescope be modest, compared to a unique instrument, or improvements on the single telescope, for the same cost?

I suppose that using two telescopes as an interferometer would be quite a different instrument design to begin with than just two of the same.


texts: What are the prospects for follow-up observations of phosphine on Venus?

texts:
Today, it was officially announced that astronomers have detected phosphine on Venus via the $\text{PH}_3(0\to1)$ transition (Greaves et al 2020). While the line was found by both the James Clerk Maxwell Telescope and ALMA, and while the team is fairly confident that the detection is robust, follow-up observations would nevertheless be nice, particularly in other bands. Sousa-Silva et al 2020 note that phosphine has strong features in the 2.7-3.6, 4.0-4.8, and 7.8-11.5 micron bands, and while they're pessimistic about detecting phosphine in $\text{CO}_2$-dominated atmospheres around Sun-like stars using less than ~200 hours of observing time, those numbers are for exoplanets, where we'd expect substantially lower fluxes than we'd receive from Venus.
With all that in mind, what are the most promising bands to search for phosphine on Venus, in addition to to the $1\to0$ transition? Are they the three infrared bands discussed by Sousa-Silva et al, or could other trace components of the Venusian atmosphere block the signal at some wavelengths? I see that $\text{SO}_2$ was the only remotely feasible possibility for a source mimicking the observed phosphine transition, but that would require temperatures twice as high as observed.

As a side note, it's been announced that BepiColombo will use an onboard spectrometer to try to detect phosphine on Venus during two flybys of the planet en route to Mercury. The first will be on October 15, 2020, and the second will be on August 10, 2021. I haven't been able to find out more details on the planned observations, but the spectrometer (MERTIS) operates in the 7-14 micron band.


texts: Angle between earth's angular momentum and earth's axis

texts:
I think this picture is correct because for earth astronomical day is slightly shorter than solar day. (Is it a rule of thumb for planets? Where can I read such data?)

 Source

So the angle between earth's angular momentum and earth's axis(from south pole to north pole) is 23.5° and not a (180°-23.5°).

That is why observer is standing on the sun in the next picture. And the break in circle-shaped arrows is closer to the sun, then the rest of arrow.

Am I right? Thanks!

Source


texts: Suns Orbital speed and escape velocity question

texts:
This is a homework question and I don't want an answer but just want to understand what its asking for.

We are given that a star with a mass of x solar masses in our galaxy turns to a supernova and releases y amount of energy. Using this we are asked to calculate the average speed of the ejected mass.

v = sqrt(2*E_k/M) (Kinetic energy equation) gives the average speed.

Finally, the questions asks the following:

  Compare  your  result with our Sun’s orbital speed around the centre of the Milky Way galaxy. Where would you expect this material to end up?

Is it asking to solve and check that the average speed > escape velocity if the star was at the same distance from the sun? Or how far from the center of the Galaxy would it end up?


texts: Are there any double stars that I can actually see orbit each other?

texts:
If I had a nice amateur telescope†, are there any multiple star systems that I could observe over a few years or a few decades and actually see the movement of one or both of them over time?

My short human lifespan and limited telescope put heavy constraints on the orbital distance, brightness, and distance from the Sun, so I am guessing that if there are any at all, the number is probably small.

†arbitrarily defined as say 8-inch (20 cm) aperture, with a good set of eyepieces, and a sketch pad.


texts: DAMIT how do they get 3D shape and rotational trajectory of a tumbling asteroid from photometry?

texts:
This question asks about an algorithm used in Project DAMIT.
@RobJeffries' answer led me to Wikipedia's William Herschel Telescope which led me to Wikipedia's 2008 TC3 which led me to the animation 2008 TC3 Tumbling (reduced).gif which led me to https://astro.troja.mff.cuni.cz/projects/damit/asteroids/view/2508 where I see two pages listed for light curve data. I've plotted them below.
The web site says that the reconstruction of the shape and tumbling of the asteroid is done as described in their documentation page:

DAMIT asteroid models
DAMIT contains asteroid models that were derived using the light-curve inversion method developed by Kaasalainen & Torppa (2001) and Kaasalainen et al. (2001), combined with other inversion techniques in some cases. Each model in DAMIT references the original paper(s) where it was published. Please note that the models presented in DAMIT may differ from those published in the original papers. The main reason for this is a limited dataset used in the original publication and/or a narrow range of periods scanned during the inversion.

Question: As both parts of the paper are paywalled in Icarus is it possible to generate a straightforward description of the basic idea behind how this reconstruction process generates a shape from an $I(t)$ plot?
For delay-doppler radar observations there is a rich set of data available, but here there is only intensity vs time. How can a 3D shape be unambiguously determined from what looks like a pretty chaotic set of data?
I plotted the data just for kicks.

Source


texts: How can a supernova affect black hole in a binary system?

texts: Suppose in a binary stars system there is a dying star and a companion black hole as they orbit around each other. My question is what will possibly happen to the black hole if the partner goes supernova? I understand that the kinetic energy from the supernova cannot destroy the black hole.


texts: What's the mass of the interstellar neighborhood of the Sun?

texts:
What's approximatively the mass of the interstellar neighborhood of the Sun ?
(for example the neighborhood of radius 50 light-years).

Remark: The mass of the observable matter should be completed by the mass of the "dark matter".


texts: Is most hydrogen in the universe in the form of plasma, atomic neutral hydrogen, ionized hydrogen, or molecular?

texts:
I have had trouble finding an answer somewhere....
Some places say most hydrogen is plasma, such as the stuff stars are made of (mostly) and the 'warm-hot intergalactic plasma'.
Other places say neutral atomic hydrogen (H(I) to astronomers), such as the stuff in the interstellar medium, is the most common...


texts: Python controllable amateur astrophotography cameras?

texts:
I would like to read further about any successes that amateur astrophotographers (or professionals) have had with USB CCD cameras that are controlled by Python scripts. I'd like to script the setting of exposure time, triggering of exposures, downloading and processing of images.

Ideally this would be computer platform-agnostic.

I've recently asked Python interface for DMK 23U274 USB camera for astrophotography but the more I read about that the more I think that it's going to be tough running that particular camera from a Python script.

Where can I read further about this being done, or at least what solutions are known to exist?


texts: Will the Sun's solar wind push a permanent magnet out of our solar system?

texts: If you were place a strong permanent magnet into the solar wind, like a 1 inch cube neodymium magnet, would the charged particles of the solar wind colliding with the magnet's magnetic field push the magnet out of our solar system, that being if it does not encounter any planets or objects in its path?


texts: How is the Lithium Depletion Boundary used to determine the age of a stellar cluster?

texts:
According to my understanding of Soderblom et al. (2014), lithium ages of stars are determined as follows:

Determine lithium abundance from equivalent width measurement of Li$_{\mathrm{I}}$ transitions at 6708 angstroms for all stars in a coeval group.
Plot all stars in group on color-magnitude diagram, with each star labeled as Li-rich or Li-poor.
On plot, look for the boundary where the stellar population transitions from depleted to undepleted. That is the Lithium Depletion Boundary (LDB).
Use the luminosity of the LDB and the age-LDB luminosity relationship to determine the age of the stars in the group.

What is the age-LDB luminosity relationship, and what are its physical origins?


texts: How to make a star chart from entries in a Bright Star Catalogue?

texts:
I know very little in astronomy, but I want to use the data in a Bright Star Catalogue to create star map projections for a specific time and place.

For example one line is

{ "Dec": "-33° 31′ 46″", "HR": "13", "K": "4850", "RA": "00h 08m 03.5s", "V": "5.68" },

How would I convert this to an $x, y$ point on a printed star chart that could be used for viewing the sky at a specific time and place?


texts: Is any consensus forming on the solution to the "Lithium Problem"?

texts: The "Lithium Problem" relates to the fact very-low-metallicity stars appear to have a Li/H ratio approximately one third of what would be expected. The ratio should be the same as the prediction from Big Bang nucleosynthesis theory. A possibly related problem is that the ⁶Li/⁷Li ratio is several orders of magnitude too high.


texts: Was looking at the sky and I see a satellite , turned around and saw another light , but this light was pulsating like a strobe light , definitely not a plane , next thing I know the light goes out and was not seen again , could this be a dying star , I know what satellites and planes look like in the sky , but I have never seen anything like this , it just went dark after being super bright


texts: I am an amateur astronomer please correct if any of my understandings are wrong. We all know that from the Hubble's ultra deep field image the most distant galaxies which were created shortly after big bang looked to be red shifted. This is because of the process of expansion of the universe these lights are reached its highest visible wavelength. So in near future (in terms of astronomy) the galaxies which appears to be normal today become red shifted?  and those are already appeared as red shifted become invisible? If it become invisible still can we see it through infrared telescopes right?


texts: What are the last images from the Galileo orbiter before impacting Jupiter?

texts:
NASA's Galileo orbiter at Jupiter ended its mission in 2003 by intentionally dive into the gas planet. Did it take and transmit any close up images before it ceased to function? If not, why? Are there any images from Galileo, or its separate impactor probe, which show the Jovian clouds from close enough range that their topology is discernible?

On all images I've seen, Jupiter looks like a perfect sphere because of its huge size and far distances from which it has been imaged. But if two spacecrafts have dived into it, there should be close up images of its clouds, right?


texts:
Below this question there is a comment that caught my interest:

  First, there's a misconception. Compressing a body does not increase the force of gravity on outer-lying masses. That's Gauss's famous divergence theorem.

I understand that one can use the divergence theorem to address (derive) the shell theorem - one consequence of quick is that a particle inside a spherically symmetric shell experiences no net gravitational force from the shell, but this seems different as it refers changes in average density of a body and gravitational forces on outer-lying masses.

So I'd like to understand better: What does Gauss' divergence theorem say about compression of a body under self-gravitation?

For reference, this answer covers the shell theorem nicely.


texts: Can there be an object with planetary discriminant between Ceres and Neptune?

texts:
The planetary discriminant is a measure of how dominant a body is within its region of the solar system. For (true) planets, it is $>10000$ and for dwarf planets it is $<1$. (See this answer to "How many planets are there in this solar system?" which explains the related details.)

Is it possible, given what has already been observed about our solar system, for there to be an object with  "planetary discriminant" µ between that of Ceres and Neptune?   In other words, could the clear cut line between planets and dwarf planets get fuzzier?

Obviously it would have to be a massive body pretty far out.  Is there a region in the solar system which could be devoid enough of many small objects, which also could be home to a large enough body that we also haven't observed yet?   How does the math work out?


texts: Do interstellar asteroids decelerate and eventually stop?

texts:
I do wonder, do interstellar asteroids eventually stop at one point in space after they gradually decelerate (or) even do they decelerate?

Though there is no air like on earth and thus asteroids will not be affected by frictional forces, do they have friction with gravitational forces against their trajectories?

If it is so, they might eventually stop. Are there any known objects like that?


texts: What are the concrete technical arguments supporting the idea that the wave function of the universe can be written as partition function?

texts:
In this talk, the not yet settled down idea that the wave function of the universe could potentially be written as  the partition function of a scale invariant statistical field theory is mentioned:

$$
\Psi[g] = Z[g] = \int D(\text{Fields}) e^{-S[g,\text{Fields}]}
$$

If our universe were AdS, this relation could already be well enough explained by the AdS/CFT correspondence, but as our expanding universe correspond to a dS geometry, things are less clear.

What are the concrete technical arguments, ideas, or hints that this relationship should hold for our dS universe too? What work has already been done on this?


texts: Transition of Domination in the Universe

texts: While deriving the epoch of matter-radiation equality, we assume the transition from radiation dominated universe to matter dominated universe as instantaneous. But how instantaneous is this transition really?


texts: Determining the extinction by counting stars?

texts:
Hi I'm a highschool student studying astronomy at school.
I learned that one can determine how much a luminosity of a star is reduced by counting stars, but I can't understand how it works. My textbook has the following equation:

$\Delta m=2.5 \log(\frac{N}{N_0})$ or also written as $\Delta\log N=0.4\Delta m$
, where N is a number of stars and m is the magnitude.

The textbook says that by comparing the number of visible stars from the inside of an interstellar cloud with that of stars from the outside of the cloud, one can determine how much the luminosity is decreased using that equation.

I have no idea how the equation is created. I searched it on google but I only found this pdf: http://rpi.edu/dept/phys/observatory/obsastro9.pdf
Can anybody explain it for me?


texts: Is any meteorite known to come from a comet?

texts: Comets are mostly icy but they should have some rocky components too, right? I wonder if there's any rocky piece of a former comet among collected meteorites. Is it possible today to identify a meteorite as having cometary origin? Or has surviving pieces from comet impacts been too rare (or violent vapourizing) events?


texts: What is the precise definition of a moon?

texts:
With the recent discovery of Saturn's 20 new moons (elevating its position on the rank of planets with the greatest amount of moons, surpassing Jupiter), it makes me wonder: what are the requirements a celestial body has to meet to be considered a moon?

Are there any limitations in size, shape or even orbit?


texts: North Stars of each Solar system planet?

texts:
What are the North Stars of each individual body points too?
E.g.
Earth points to Polaris.
Mars points to Deneb/Alpha Cygni.
What about Sun, Mercury, Venus, Moon, Jupiter, Saturn, Uranus, Neptune, Pluto?


texts: What is the name of the cycle whereby the lunar azimuth and altitude recur on a given day?

texts:
Like the Metonic cycle, except for position in the sky, not phase.

Original question: If I look up at the moon tonight, how long before it is in the same apparent position, and same phase, again?

I realized I can calculate this myself, if only I know two piece of information. Unfortunately I do not know the name of the second.

My question should be answered by the product of:

the Metonic cycle, and
the cycle where the moon's azimuth and altitude recur on a given day

What is the name of this second cycle?


texts: Origin of the magnetic field of neutron stars

texts: It seems a little counter intuitive that neutron stars possess such strong magnetic fields. Its electric charge is presumably zero, so however fast it spins, it shouldn't generate any magnetic field. Or is it due to the electric charges of quarks or their intrinsic spins?


texts: Why are these objects moving at Vastly Different Speeds along the same orbit?

texts:
UPDATE: The on-line simulation seems to be working beautifully now! I'd recommend anyone to go back and take another look to enjoy both the mathematical beauty of orbital mechanics, and the aesthetics of the solar system visualization!

New York Times article Visualizing the Cosmic Streams That Spew Meteor Showers links to a solar system viewer that allows one to visualize aspects of meteor-shower-inducing comet orbits by Ian Webb.

Now, astronomers and engineers have created an animation that lets you witness the entire journey. Using data from the Cameras for Allsky Meteor Surveillance, a network of about 60 cameras pointed at the sky above San Francisco Bay, researchers have recorded more than 300,000 meteoroid trajectories since 2010. They plan to use the data to confirm more than 300 potential meteor showers that scientists have observed, but not verified.
“Each dot that you see is a shooting star that was captured by one of our cameras,” said Peter Jenniskens, an astronomer at the SETI Institute and NASA Ames Research Center in Silicon Valley, Calif., who runs CAMS. His interactive transforms meteor showers like the Geminids and the Orionids into shimmering rivers of space rocks. Viewers can pinpoint the moment the Lyrids or Eta Aquarids light up the night by watching when their streams intersect with the Earth’s orbit, shown in blue. There is even an option to see all the meteor showers at once, making it look like a meteor hurricane.

I need some help understanding what I'm looking at. When I first open it up I believe I see a number of objects following the same general hyperbolic (or very elliptical) orbit. What bothers me is that some seem to zip past very fast, some seem to crawl slowly, and some are moving at intermediate speed. If they are all associated with one primary comet, and follow similar paths in this large (roughly 10 AU) view, shouldn't they have at least roughly similar velocities?
Edit: I've snapped screenshots from 30-10-2017 to 04-11-2017 at a speed setting of 0.005 and made two GIFs below The second one is annotated with a red, green, and blue arrow indicating three objects (slow, medium, and fast) following nearly the same orbit with at least a factor of 10 different speeds between them.
I have replayed viewing from different angles, they follow nearly the same orbit in 3D, all the way around the sun and back into space - it is not related to a particular view.
I believe this to be completely unphysical!

 Red, Green Blue (slow to fast)


texts: What if Jupiter and other gas planets suddenly disappear?

texts:
What will happen to us?

Jupiter, for example, take away comets from their path, so they will not hit earth.

What else can/cannot happen? Have they any purpose for us?


texts: Naming convention for multiple star systems

texts: Okay, so I've seen different notations for the stars in β Capricorni. Some sources state that the stars are Aa, Ab1 and Ab2, Ba, and Bb, while others say that they are Aa, Aba and Abb, Ba, and Bb. So, what is the proper way to name stars in a multiple star system, and are there any exceptions to this convention?


texts: can gravity be faster than light in some specific cases?

texts:
This is a follow up question from
If an event occurs at a point in space time what will an observer experience first, it's gravity or the light from it?

This https://en.wikipedia.org/wiki/Alcubierre_drive article on Wikipedia about Alcubierre drive says that faster than light travel is possible by manipulating space, though physically not possible, but if we transport a massive object using this drive, will the disappearance of the object's gravitational field be observed first or the disappearance of the object (EM Radiation) observed first? In simple words can gravity be faster than light in some cases?


texts:
Follow this question. If a star at the same distance from us as, say, Proxima Centauri had exploded as a Supernova 4 years ago (I know, it can't explode as supernova, let's say it can)...

How bright will it be?

It will impact us (life on earth and/or technology)?

What about Sirius?


texts: Detecting the Chicxulub impactor, right now

texts:
Say an asteroid identical in all ways to the Chicxulub impactor (size, mass, materiel, orbital type, etc) was about to hit us.  (Again!)

As of exactly early 2018,

given our known instruments and indeed our known watch-out-for-asteroid-collisions systems,

in fact,

when would it be a reasonable certainty, that we would know about it coming?  (Only days before hand?  Weeks - months - years - decades?)

Are there any gotchya factors?

(Such as ... we'd likely miss it if it came from 'above'? 'from the direction of the sun'?? etc.)

Any perhaps current limiting use cases?

(Something like ... "anything over K km we'd know for sure Y years ahead of time, smaller than that no chance...")

I guess, some folks on this list are familiar on a day to day basis with our "known instruments and indeed our known watch-out-for-asteroid-collisions systems" ...  but to the layman it's an unknown!

And technology is very topical, of course.  I guess the answer is changing in a Moore's Law -ish way from year to year.  (For example, would the JWST affect this calculation, or has nothing to do with the issue?  What about other systems or single instruments coming online soon?)


texts: Creating a basic "fixed" solar system to host a 3D space travel simulation

texts:
I'm trying to simulate a virtual/imaginary "solar system" in software--just a hobby project for now. Unfortunately this has made me realize exactly how much math I've forgotten since college.

Complete accuracy isn't important, and I'm not looking to do anything sophisticated... no need for multi-body calculations, just a star and a planet will do. I just want something that a lightweight simulation or a game might do.

I'll have a configuration file with some basic starting parameters for each planet. At the start of the simulation, time=0 seconds, all planets would be lined up in a row (planning on just placing them on the same axis at their perihelion distance from the star). I'd like the planets to move around their orbits at the correct speed given the parameters supplied. So if I decide to set time = 1e10, I need to be able to calculate the x and y positions of each planet in their orbit at that precise time.

I'm flexible on WHICH parameters need to be provided. So if this becomes easier using some other method of defining the orbit, I'm open to it. Right now I'm thinking perihelion, mass, and time elapsed.

(Since this is a 3D simulation, eventually I'd also like to work inclination in, but I'm trying to start off simple for now, so inclinations will all be zero.)

Here's some sample parameter data below in case it helps provide a better example.

Star mass = 2.00e30

Planet mass = 3.30e23

Planet perihelion = 5800000

(Ex. Where would this planet be, in X/Y coordinates, at time=x?)

If someone posts a formula I can just plug in I won't complain. But if I could just be pointed in the right direction for what to learn or refresh my memory on, I'd like to try and figure this out myself. So far I've been looking at Kepler's 3rd Law equations but I'm not sure if that's a good place to start. Feeling a little guilty that I seem to have forgotten virtually all math I learned in college just over a decade ago, and I kind of want to reverse some of that decay.  Hopefully this makes sense!


texts: Cosmology calculator where curvature density $\Omega_k$ can be independently set?

texts:
I am looking for a cosmology calculator that does not have the default that
$$\Omega_k = 1 - (\Omega_r + \Omega_m + \Omega_{\Lambda}).$$
I particularly want to run
$$\Omega_r = \Omega_m = \Omega_{\Lambda} = 0, \ \text{and} \ \Omega_k = -1.$$
Can this be done?


texts: Stars can be plotted on an HR diagram, on which a main sequence is apparent, and stellar evolution can be plotted on on such a diagram as a function of mass. Is there an analog for galactic evolution? Are there "main sequence galaxies"?


texts: Exactly how does Canis Minor look like a dog?

texts:
Here's what Canis Minor looks like.

To me, all I see is two stars. Canis Minor is a constellation of the giant Orion's hunting dog. Two stars can give quite a meaning. Two stars can mean a stick, a telescope, et cetera. But how could that be interpreted as a dog?

Since this is a Greek constellation, are there any sources that explain why ancient Greeks considered those two stars to represent a dog?


texts:
First, I'd like to take the definition of a "double-planet" as two bodies orbiting each other where the center of gravity is not inside the larger body. Also, the system would have to fill other planet requirements (like emptying it's own orbital area around the star).

Now, let's say that the "binary system" is in an orbit close enough to a star to be tidally locked to the star. How would the tidal effects of the star's gravity effect the orbit of the planets around each other??

Let's take an example of a "double-planet" (of $0.075$ and $0.030\:\mathrm{M_{Earth}}$ with a separation of $1.17 \times 10^6\:\mathrm{km}$ orbiting their CM in about $450\:\mathrm{days}$. They are $0.085\:\mathrm{AU}$ from a star of mass $0.35\:\mathrm{M_{Sun}}$ and thus orbit the star in $15.3\:\mathrm{days}$. The planetary rotation/co-orbital period is much longer than the orbital period around the star, so I would think that the planets would have characteristics of a lone TL planet.

I am wondering how such a system would evolve over time. Would someone on the surface of one of the planets experience experience night and day in 15.3 day cycles? Would the difference in tidal effects of the star on the different sized planets cause the orbit to "precess" or have some other effect?

Imagine designing a long term calendar for this system!!


texts: Can I see Uranus and Neptune with a household telescope?

texts: Can I see Uranus and Neptune with an iOptron telescope with a 600mm focal length. If so, can I expect to see them in colour, or simply as white objects?


texts: Have Pluto or any of its moons been mapped?

texts: I was looking over some of the data for the terrestrial planets, and noticed that Venus, despite its cloud covering, had been mapped by the Arecibo Observatory. Also that other planets such as mars, and some of the Jovian moons were mapped by the Voyagers. So, do any maps exist for Pluto or its moons?


texts: How do we detect if a planet has a liquid core?

texts:
In case of Earth, we have many hints about the internal structure of our planet, from what I know, the most important of which is analyzing seismic waves.

Do we have any instruments to detect if other solid planets, such as Mars or Venus, have solid or liquid core? Is it possible using remote sensing?